1. Field of the Invention
The present invention relates to a broadband mobile communication system. More particularly, the present invention relates to a device and method for measuring received signal power in a receiver of a mobile communication system where narrowband interference is present.
2. Description of the Related Art
A mobile communication system provides a communication service to a terminal with assigned wireless frequency resources. However, a variety of possible interference in the wireless environment may cause performance degradation of the mobile communication system and may also disable the system in a worst case scenario. Thus, there is a need to provide a solution to address the interference.
Interference in a mobile communication system is generally divided into interference between the same frequencies and interference between nearby frequencies. The interference between the same frequencies includes interference between base stations and interference caused by another system such as an illegal radio station. The interference between nearby frequencies includes interference between base stations in the same system using nearby frequencies and interference between adjacent systems.
The most significant interference in the current broadband mobile communication system is perhaps strong narrowband interference caused by another system using the same frequency resources. The narrowband interference in the mobile communication system may cause system performance degradation and communication blackout.
On the other hand, the mobile communication system measures power of received signals to allow system control based on states of the signals. Specifically, accurate power measurement of the received signals allows effective calculation of reverse link load, which makes it possible to control user access and transfer rates in the reverse link. Accurate received signal power measurement also contributes to an increase in the mobile communication system capacity and also to effective resource management. The configuration of a receiver in the mobile communication system, which measures received signal power, will now be described in detail with reference to FIG. 1.
FIG. 1 is a block diagram illustrating a conventional receiver of the mobile communication system.
As shown in FIG. 1, the receiver includes an antenna 10, a received RF processor 20, a modem 30 and a received power measurement unit 40. The received RF processor 20 converts an RF signal received through the antenna 10 into a baseband signal in order to demodulate the received RF signal. The modem 30 demodulates the converted baseband signal. The received power measurement unit 40 measures power levels of the received signal. The received RF processor 20 filters the received RF signal to obtain a signal in a desired band, and converts the obtained signal into an intermediate frequency signal and then into a baseband signal. The received power measurement unit 40 measures received signal power for performing a Rise Over Thermal (ROT) function for controlling user access and transfer rates in a communication system such as a Code Division Multiple Access 200 First Evolution Data Only (CDMA 2000 1x EV-DO).
Broadband and narrowband signals coexist in such a receiver. FIG. 2 is a graph showing frequency characteristics of the coexisting broadband and narrowband signals in the conventional receiver. It can be seen from FIG. 2 that a broadband signal 50 and narrowband signals 61, 62 and 63 share the same frequency resources. However, the narrowband signals serve as interference signals to the broadband signal. If high power signals such as the narrowband interference signals use the same frequency resources used by the broadband signal, communication blackout is caused. Receipt of the narrowband interference signals having high power also causes abnormal measurement results. To overcome these problems, attempts have been made to use interference elimination filters for removing narrowband interference signals interfering with the system, thereby reducing system performance degradation. Despite these attempts, there are still difficulties in accurately measuring the received signal power.